A thin film transistor (TFT) is used in diverse fields, more particularly, as a switching and driving device in flat panel display devices such as a liquid crystal display (LCD), an organic light emitting diode display (OLED display) and an electrophoretic display.
The thin film transistor includes a gate electrode connected to a gate line for transferring a scan signal, a source electrode connected to a data line for transferring a signal supplied to a pixel electrode, a drain electrode facing a source electrode and a semiconductor electrically connected to a source electrode and a drain electrode.
The semiconductor is an important element for determining a characteristic of the thin film transistor. Silicon (Si) is most widely used as such a semiconductor. The silicon is divided into amorphous silicon and polycrystal silicon according to crystal formats. Since a cost for manufacturing the amorphous silicon is low and its manufacturing process is simple. However, since charge mobility of the amorphous silicon is low, there is a limit to be used for manufacturing a highly efficient thin film transistor. Since the polycrystal silicon has high charge mobility but requires a process of crystallizing silicon, a manufacturing cost is high and a manufacturing process is complicated. A metal oxide semiconductor may be used to compensate the amorphous silicon and the polycrystal silicon. The metal oxide semiconductor does not require an additional process for crystallizing the semiconductor and may raise the charge mobility according to manufacture processes.
In particular, when a solution process is adopted in manufacturing the metal oxide semiconductor, there is an advantage that it is possible to satisfy the charge mobility required in a display device and other electrical characteristic, remarkably reduce the manufacturing cost, and evenly form a metal oxide semiconductor thin film in a large area.